Design of a smart microgrid with small-scale hydro generation: a practical case study

Microgrids are local electric grids integrating distributed generation and consumption, energy storage and management and power control. They can be an alternative for the energy supply of a house, a building, a small village or a wider region. Small-scale hydropower, in the range of 5 kW, consists of distributed generation systems gaining increasing interest. These so-called pico-hydro systems are becoming popular since they can take advantage of the integration of low-power wind generators and photovoltaic (PV) inverters, which are widely available at competitive prices. Thus, pico-hydro systems are not only relevant for energy generation in off-grid systems in remote areas but also for new contexts where the utility grid is available. This paper presents the design of a smart microgrid with small-scale hydro generation. It is a practical case study with the integration of two grid-connected pico-hydro turbines: a low-head propeller turbine and a water wheel. The microgrid was designed and implemented in a small museum: Casa da Seda (House of Silk). The energy generation is based on the complementarity between hydro and PV. The microgrid can operate in both grid-connected and islanded modes and feeds the House of Silk loads. The connection of both pico-hydro turbines into the microgrid is based on the integration of wind generators and PV inverters.Las microrredes son redes eléctricas locales que integran generación y consumo distribuidos, almacenamiento y gestión de energía y control de potencia. Pueden ser una alternativa para el suministro de energía de una casa, un edificio, un pueblo o una región más amplia. Las pequeñas centrales hidroeléctricas, hasta 5 kW, son sistemas de generación distribuida que están ganando un interés creciente. Estos llamados sistemas pico-hidráulicos se están volviendo populares ya que pueden aprovechar la integración de generadores eólicos de baja potencia e inversores fotovoltaicos, ampliamente disponibles y a precios competitivos. Estos sistemas no solo son relevantes para la generación de energía en sistemas desconectados de la red en áreas remotas, sino también para nuevos contextos donde la red pública está disponible. Este artículo presenta el diseño de una microrred inteligente con generación hidroeléctrica a pequeña escala. Es un estudio de caso práctico con la integración de dos turbinas pico-hidráulicas conectadas a la red: una turbina de baja altura y una rueda hidráulica. La microrred fue diseñada e implementada en un pequeño museo: La Casa da Seda. La generación de energía se basa en la complementariedad entre hidroeléctrica y fotovoltaica. La microrred puede funcionar tanto en modo conectado a la red como en modo de isla y alimenta las cargas del museo. La conexión de ambas turbinas pico-hidráulicas a la microrred se basa en la integración de generadores eólicos e inversores fotovoltaicos.This work was supported by European Union under the Project BIOURB-NATUR; the Polytechnic Institute of Bragança and the CYTED Thematic Network 518RT0558 - Ciudades Inteligentes Totalmente Integrales, Eficientes y Sostenibles.info:eu-repo/semantics/publishedVersio

Does Curvature Enhance Forecasting?

In this paper, we analyze the importance of curvature term structure movements on forecasts of interest rate means. An extension of the exponential three-factor Diebold and Li (2006) model is proposed, where a fourth factor captures a second type of curvature. The new factor increases model ability to generate more volatile and non-linear yield curves, leading to a significant improvement of forecasting ability, in special for short-term maturities. A forecasting experiment adopting Brazilian term structure data on Interbank Deposits (IDs) generates statistically significant lower bias and Root Mean Square Errors (RMSE) for the double curvature model, for most examined maturities, under three different forecasting horizons. Consistent with recent empirical analysis of bond risk premium, when a second curvature is included, despite explaining only a small portion of interest rate variability, it changes the structure of model risk premium leading to better predictions of bond excess returns.

Control of grid-connected inverter output current: a practical review

The number of grid-connected inverters is growing due to the expansion of the use of renewable energies (RE) systems and this may affect grid power quality and stability. Some control algorithms reduce injected current harmonics and add new possibilities to the converter. This paper implements and analyses the proportional integral (PI) controller in the synchronous frame and the proportional resonant (PR) controller with and without the harmonics compensators (HC). All these control strategies have proven to be effective and robust. However, the PR+HC controller presents better output current quality. The PI and PR controllers have similar performances. This work also compares the harmonic content of the current with the IEEE 1547 reference and with three commercial inverters from different manufacturers.info:eu-repo/semantics/publishedVersio

Analyses of MPPT algorithms in real test conditions

Maximum Power Point Tracking (MPPT) algorithms are of major importance for optimized yield in gridconnected PV systems. Many algorithms have been investigated. However, most of the works compare these algorithms based on a literature review or on simulation. This paper presents an experimental analysis of MPPT techniques: two of the simplest (Perturb & Observe and Incremental Conductance) and two of the most complex (Fuzzy Logic Controller and Particle Swarm Optimization). The results are carried out in real test conditions, with and without shadow. The power converter is based on a boost converter and a voltage source inverter. The control is implemented using Simulink® and dSPACE 1103 real-time controller board. Moreover, the MPPT techniques of three commercial string inverters are also analysed.info:eu-repo/semantics/publishedVersio

Glycome dynamics in T and B cell development: basic immunological mechanisms and clinical applications

Glycans cover the surfaces of all mammalian cells through a process called glycosylation. Nearly all proteins and receptors that integrate the intricate series of co-stimulatory/inhibitory pathways of the immune system are glycosylated. Growing evidence indicates that the development of the immune system at the origins of T and B cell development is tightly regulated by glycosylation. In this opinion, we hypothesize that the glycome composition of developing T and B cells is developmentally regulated. We discuss how glycans play fundamental roles in lymphocyte development and how glycans early define T and B cell functionality in multiple aspects of adaptive immunity. These advances can provide opportunities for the discovery of novel disease factors and more effective candidate treatments for various conditions.This work was funded by the EU (ERC, GlycanSwitch, Grant Agreement N° 101071386). Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Funded by the European Union (GlycanTrigger, Grant Agreement N°: 101093997. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or European Health and Digital Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. M.M.V. and E.L-G. received funding from the Portuguese Foundation for Science and Technology (FCT) of the Portuguese Ministry of Science, Technology and Higher Education (M.M.V.: PD/BD/135452/2017, COVID/BD/152488/2022; E.L-G.: UI/BD/152866/2022)

Protección contra sobretensión para la generación pico-hídrica conectada a la red mediante inversores fotovoltaicos

Very small-scale hydropower plants are environmentally friendly and renewable resource-based innovative solutions. The interest in pico-hydro systems (up to 5 kW) has increased significantly from the first stand-alone applications, at remote sites, to the distributed generation, with the injection of generated energy into the grid. Recently, there have been advances in the grid connection of these systems using off-the-shelf components, namely photovoltaic inverters. Therefore, pico-hydro systems have gained an enormous potential in distributed generation, particularly in the context of microgrids. However, in situations of over-power, or whenever the generator is under no load, e.g. when the grid fails, there is a need for effective over-voltage protection, as in small wind turbines. This paper proposes two over-voltage protection circuits, designed to ensure the integration of pico-hydro turbines connected to the grid using conventional photovoltaic microinverters and string inverters, for power ranges of 300 W and some kW, respectively. Extensive tests were performed on an emulation platform and a workbench using these two different over-voltage protection circuits. One is designed to connect the generators of water wheels to the grid and the other to connect 1,500 W generators of water turbines. The experimental results demonstrated the performance of the proposed over-voltage protection circuits in four different situations. Both avoid irreversible damages of generators, photovoltaic microinverters and string inverters in the context of the above-described grid connection approach.Las centrales hidráulicas, a muy pequeña escala, son soluciones innovadoras basadas en recursos renovables y respetuosas con el medio ambiente. El interés en los sistemas pico- hidráulicos (hasta 5 kW) ha aumentado significativamente desde las primeras aplicaciones independientes en sitios remotos, hasta la generación distribuida, con inyección de energía en la red. Recientemente, han surgido avances en la conexión a la red, utilizando componentes estándar como los inversores fotovoltaicos. Sin embargo, en situaciones de exceso de potencia, o cuando el generador no tiene carga, por ejemplo, cuando falla la red, existe la necesidad de protección frente a la sobretensión. Este artículo propone dos circuitos de protección frente a la sobretensión, diseñados para conectar turbinas pico-hidráulicas a la red, utilizando microinversores fotovoltaicos e inversores de cadena, para rangos de potencia de 300 W y algunos kW, respectivamente. Uno de ellos está diseñado para conectar los generadores de ruedas hidráulicas a la red y el otro para conectar generadores de turbinas hidráulicas de 1.500 W. Se realizaron extensas pruebas en una plataforma de emulación y en un banco de trabajo utilizando estos dos circuitos de protección contra sobretensión. Los resultados experimentales demostraron el rendimiento de los circuitos de protección, respecto a cuatro situaciones diferentes. Además, ambos evitan daños irreversibles en los generadores y microinversores e inversores de cadena, dentro del contexto del enfoque de conexión a la red descrito anteriormente.The authors would like to thank: the CYTED Thematic Network 518RT0558 ”Ciudades Inteligentes Totalmente Integrales, Eficientes y Sostenibles”; FCT (Foundation of Science and Technology, Portugal) for the financial support through the contract SAICT-POL/24376/2016 (POCI-01-0145-FEDER-024376); and Gabriela Ribeiro, for her contributions for the development of this work.info:eu-repo/semantics/publishedVersio

A new approach for speed estimation in induction motor drives based on a reduced-order extended Kalman filter

This paper presents and proposes a new approach to achieve robust speed estimation in induction motor sensorless control. The estimation method is based on a reduced-order extended Kalman filter (EKF), instead of a full-order EKF. The EKF algorithm uses a reduced-order state-space model structure that is discretized in a particular and innovative way proposed in this paper. With this model structure, only the rotor flux components are estimated, besides the rotor speed itself. Important practical aspects and new improvements are introduced that enable us to reduce the execution time of the algorithm without difficulties related to the tuning of covariance matrices, since the number of elements to be adjusted is reduced

Low-cost I-V tracer for photovoltaic modules and strings

This paper presents new developments of a robust and low-cost instrument-less than 600 (sic)-for monitoring and processing I-V and P-V characteristics of photovoltaic (PV) modules and high voltage strings. The characteristics can be traced on an oscilloscope or using a developed a LabVIEW application. It is a simple instrument because only fundamental electronic circuits are used. The equipment consists of a flexible configuration, developed from a previous work, based on a fast varying load based on a power MOSFET. The MOSFET was controlled by means of suitable gate-source voltage control signal in order to improve the tracing of I-V and P-V characteristics on an oscilloscope. The contribution of this work includes new developments of a previous I-V tracer in order to be use with high voltage strings and a low-cost DAQ monitoring system based on two applications developed in LabVIEW-one for PV modules and the other for PV strings. On the other hand, the robustness for high voltage strings was strongly improved in view of field tests for fault diagnosis analysis. Experimental results obtained with the new instrument are presented with modules and different strings available with voltages up to 1000 volt

Movimentos da Estrutura a Termo e Critérios de Minimização do Erro de Previsão em um Modelo Paramétrico Exponencial

In this paper, we study how different choices of loadings affect forecasting in the exponential term structure model proposed by Diebold and Li (2006). The loadings are defined through a specific parameter lambda which controls both the decaying speed of the slope as well as the maximum of the curvature factors. In particular, adopting a database including Brazilian fixed income future contracts (ID future), we analyze four different rules of choices depending on metrics that minimize forecasting errors, for different forecasting horizons. We conclude that the optimal rule changes for different regions of ID future maturities/different forecasting horizons, indicating that the choice of how movements will be parameterized in this exponential model should be done with care, tailored for each particular application of the model.